1. Field of the Invention
The present invention relates to a method for recording and reproducing images of objects made by high energy radiation. It relates especially to a method for manufacturing a cesium halide storage phosphor, particular phosphors and a storage phosphor panel containing them.
2. Discussion
A well-known use of phosphors is in the production of X-ray images. In a conventional radiographic system an X-ray radiograph is obtained by X-rays transmitted image-wise through an object and converted into light of corresponding intensity in a so-called intensifying screen (X-ray conversion screen) wherein phosphor particles absorb the transmitted X-rays and convert them into visible light and/or ultraviolet radiation to which a photographic film is more sensitive than to the direct impact of X-rays.
According to another method of recording and reproducing an X-ray pattern disclosed e.g., in U.S. Pat. No. 3,859,527 a special type of phosphor is used, known as a photostimulable phosphor, which being incorporated in a panel, is exposed to incident pattern-wise modulated X-ray beam and as a result thereof temporarily stores energy contained in the X-ray radiation pattern. At some interval after the exposure, a beam of visible or infra-red light scans the panel to stimulate the release of stored energy as light that is detected and converted to sequential electrical signals which are can be processed to produce a visible image. For this purpose, the phosphor should store as much as possible of the incident X-ray energy and emit as little as possible of the stored energy until stimulated by the scanning beam. This is called xe2x80x9cdigital radiographyxe2x80x9d or xe2x80x9ccomputed radiographyxe2x80x9d.
The image quality that is produced by a conventional as well as by a digital radiographic system depends largely on the construction of the phosphor screen. Generally, the thinner a phosphor screen at a given amount of absorption of X-rays, the better the image quality will be. This means that the lower the ratio of binder to phosphor of a phosphor screen, the better the image quality, attainable with that screen, will be. Optimum sharpness can thus to be obtained when screens without any binder, are used. Such screens can be produced, e.g., by physical vapor deposition, which may be thermal vapor deposition, sputtering, electron beam deposition or other of phosphor material on a substrate. However, this production method can not be used to produce high quality screens with every arbitrary phosphor available. The mentioned production method leads to the best results when phosphor crystals with high crystal symmetry and simple chemical composition are used. Phosphors having complicated crystal structures as, e.g., alkaline earth fluorohalides, tend to decompose (partially) under physical vapor deposition and the production of screens in this way while using phosphors with complicated crystal structure is quasi impossible and leads to sub-optimal results. The use of alkali metal halide phosphors in storage screens or panels is well known in the art of storage phosphor radiology and the high crystal symmetry of these phosphors makes it possible to provide structured screens and binderless screens. In e.g., U.S. Pat. No. 5,055,681 a storage phosphor screen comprising an alkali metal phosphor in a pile-like structure is disclosed.
In U.S. Pat. No. 5,736,069 an alkali metal storage phosphor is disclosed corresponding to the formula:
M1+X.aM2+Xxe2x80x22.bM3+Xxe2x80x33:cZ
wherein: M1+ is at least one member selected from the group consisting of Li, Na, K, Cs and Rb,
M2+ is at least one member selected from the group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, Cu, Pb and Ni,
M3+ is at least one member selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Bi, In and Ga,
Z is at least one member selected from the group Ga1+, Ge2+, Sn2+, Sb3+ and As3+,
X, Xxe2x80x2and Xxe2x80x3 can be the same or different and each represents a halogen atom selected from the group consisting of F, Br, Cl, and I, and 0xe2x89xa6axe2x89xa61, 0xe2x89xa6bxe2x89xa61 and 0xe2x89xa6cxe2x89xa60.2.
In EP-A-174 875 and EP-B-252 991 (and U.S. Pat. No. 5,028,509), amongst other alkali metal stimulable phosphors a CsBr:Eu phosphor is disclosed, wherein the Eu is incorporated in the CsBr by firing CsBr with Europium oxide.
The alkali metal phosphors according to the disclosures mentioned above find applications for preparing structured screens and binderless screens, it would, nonetheless, be advantageous to have CsX phosphor with enhanced speed.
It is a first object of the invention to provide a method for producing a novel cesium halide phosphor, where such phosphor exhibits a high speed and thus provides more degrees of freedom for producing storage phosphor panels that combine high speed with high resolution.
It is a second object of the invention to provide a panel, containing cesium halide phosphor that exhibits a high speed combined with a high resolution.
It is a third object of the invention to provide a method for recording and reproducing images of objects made by high energy radiation.
Further objects and advantages of the invention will become clear from the detailed description hereinafter. All references cited are incorporated by reference.
The object of the invention is realized by providing a method for manufacturing a CsX:Eu stimulable phosphor, wherein X represents a halide selected from the group consisting of Br, Cl and combinations thereof comprising the steps of:
mixing or otherwise combining the CsX with between 10xe2x88x923 mol % and 5 mol % of a Europium compound, relative to the moles of CsX, the Europium compound being selected from the group consisting of EuXxe2x80x22, EuXxe2x80x23 and EuOXxe2x80x2, Xxe2x80x2 being one or more halide selected from the group consisting of F, Cl, Br and I;
heating (e.g., firing) said mixture at a temperature above about 450xc2x0 C.; and
cooling said mixture. Typically, the resulting CsX:Eu phosphor is recovered from the crucible or other suitable container in which it was prepared. The CsX:Eu phosphor resulting from such methods is novel, and provides substantial practical advantages over known CsX:Eu phosphors.
The second object of the invention is realized by manufacturing a phosphor screen containing a CsX:Eu stimulable phosphor, wherein X represents a halide selected from the group consisting of Br, Cl and combinations thereof comprising the steps of:
preparing said CsX:Eu phosphor by heating (e.g., firing) a mixture of said CsX with between 10xe2x88x923 mol % and 5 mol % of an Europium compound selected from the group consisting of EuXxe2x80x22, EuXxe2x80x23 and EuOXxe2x80x2, Xxe2x80x2 being one or more halide selected from the group consisting of F, Cl, Br and I; and
applying said phosphor on a substrate by a method selected from the group consisting of chemical vapor deposition or physical vapor deposition, including thermal vapor deposition, electron beam evaporation, magnetron sputtering, radio frequency sputtering and pulsed laser deposition or atomization techniques such as spray drying, thermal spraying, etc.
The second object of the invention is also realized by manufacturing a phosphor screen containing a CsX:Eu stimulable phosphor, wherein X represents a halide selected from the group consisting of Br, Cl and combinations thereof comprising the steps of:
bringing multiple containers of said CsX and an Europium compound selected from the group consisting of EuXxe2x80x22, EuXxe2x80x23 and EuOXxe2x80x2, Xxe2x80x2 being one or more halide selected from the group consisting of F, Cl, Br and I in condition for vapor deposition; and
depositing, by a method selected from the group consisting of chemical vapor deposition or physical vapor deposition, including thermal vapor deposition, electron beam evaporation, magnetron sputtering, radio frequency sputtering and pulsed laser deposition or atomization techniques such as spray drying, thermal spraying, etc, both said CsX and said Europium compound on a substrate in such a ratio that on said substrate a CsX phosphor, doped with between 10xe2x88x923 mol % and 5 mol % of an Europium compound, is formed.
The third object of the invention is realized by providing a method for recording and reproducing images of objects made by high energy radiation comprising the steps of:
exposing a panel containing a CsX:Eu stimulable phosphor, wherein X represents a halide selected from the group consisting of Br, Cl and combinations thereof, including between 10xe2x88x923 mol % and 5 mol % of a Europium dopant, said dopant originating from a
Europium compound selected from the group consisting of EuXxe2x80x22, EuXxe2x80x23 and EuOXxe2x80x2, Xxe2x80x2 being one or more halide selected from the group consisting of F, Cl, Br and I, with X-ray radiation for storing energy in said phosphor,
stimulating said panel with stimulating radiation having a wavelength between 500 nm and 1100 nm, releasing said stored energy as stimulated radiation and
collecting said stimulated radiation.